Liquid crystal display devices are currently in wide use as a thin display. Liquid crystal display devices of general use are a twisted nematic (TN) type and a super twisted nematic (STN) type. In producing these liquid crystal display devices, as disclosed in JP-B-62-38689 an alignment layer is necessary for allowing a liquid crystal interposed between two substrates with transparent electrodes, to align in a particular direction relative to the substrates. Further in the liquid crystal display devices of TN type and STN type, the liquid crystal must be aligned in inclination, i.e. at a pretilt angle relative to the substrate surfaces. This needs to be achieved by the liquid crystal-aligning agent used. The pretilt angle is required to be 4 to 8.degree. in, for example, the STN type. As the liquid crystal-aligning agent capable of achieving such a high pretilt angle, there are mentioned a polyimide precursor solution as described in JP-A-1-177514 and a soluble polyimide solution as described in JP-A-3-261915. In the liquid crystal display devices produced using such a liquid crystal-aligning agent, however, there are problems that the pretilt angle is not sufficiently stable and decreases in a high-temperature environment of 80.degree. C. or higher, etc., inviting poor display.
As a different method for achieving a high pretilt angle, there is introduction of siloxane structure as described in JP-A-3-164714. In this method, however, introduction of a siloxane structure to a high degree makes bad the alignment of the liquid crystal and, therefore, in some cases the siloxane structure can not be introduced in an amount necessary to obtain a sufficient pretilt angle.
As liquid crystal display devices have come to possess improved properties in recent years, it has become necessary that materials for the alignment layer possess more properties than before. Specifically, the materials for the alignment layer must give a stable pretilt angle as mentioned above and have good electrical properties and, in the production of liquid crystal devices, must show uniform film formability, anti-rubbing property, etc. Further, since a lower temperature has come to be employed in production of liquid crystal display devices in recent years, the materials for the alignment layer must show the above-mentioned properties at levels equal to or higher than the past levels even when a firing temperature lower than 200.degree. C. is employed.